Spanish patent applications ES-A-8900495 (corresponding to British patent application GB-A-2229329) and ES-A-9102561 (corresponding to British patent application GB-A-2261778) describe systems that comprise a synchronous machine that comprises electric motors and alternator means. Normally, the motor means are fed from the network. The systems also comprise an internal combustion engine, for example, a diesel engine, that serves to provide power to the synchronous machine in the event of failure in the network, so that the alternator means can continue feeding a load. Besides, the systems described in said applications comprise a hydraulic motor, that serves to provide energy to the synchronous machine during the time that passes from the detection of a failure in the network until the internal combustion engine can provide necessary power to the synchronous machine. Likewise, the hydraulic motor can serve to start the diesel engine. In ES-A-9102561, the hydraulic motor also serves to compensate overloads.
A disadvantage of the systems described in the above patents, is that the hydraulic motor needs a certain amount of time to start to function and provide the desired power to the synchronous machine, since in an idle state the hydraulic motor remains off in order not to endure any unnecessary wear and to reduce energy consumption. This implies that it may become necessary or convenient to include relatively large inertia flywheels, to ensure that the frequency at the output of the alternator means may be maintained within some specific limits, corresponding to the established tolerance level. These inertia flywheels imply high costs and diverse practical problems, known by an average expert in the field.